Magnetic stack with laminated layer

ABSTRACT

A magnetic stack with a multilayer free layer having a switchable magnetization orientation, the free layer comprising a first ferromagnetic portion and a second ferromagnetic portion with an electrically conducting non-magnetic intermediate layer between the first portion and the second portion. The magnetic stack also includes a first ferromagnetic reference layer having a pinned magnetization orientation, a first non-magnetic spacer layer between the free layer and the first reference layer, a second ferromagnetic reference layer having a pinned magnetization orientation, and a second non-magnetic spacer layer between the free layer and the second reference layer.

RELATED APPLICATION

This application is a continuation of application Ser. No. 12/425,451filed Apr. 17, 2009 which claims priority to U.S. provisional patentapplication No. 61/104,075, filed on Oct. 9, 2008 and titled “Dual STRAMwith Laminated Free Layer”. The entire disclosures of applications No.61/104,075 and Ser. No. 12/425,451 are incorporated herein by reference.

BACKGROUND

Fast growth of the pervasive computing and handheld/communicationindustry has generated exploding demand for high capacity nonvolatilesolid-state data storage devices and rotating magnetic data storagedevices. Current technology like flash memory has several drawbacks suchas slow access speed, limited endurance, and the integration difficulty.Flash memory (NAND or NOR) also faces scaling problems. Also,traditional rotating storage faces challenges in increasing arealdensity and in making components like reading/recording heads smallerand more reliable.

Resistive sense memories are promising candidates for future nonvolatileand universal memory by storing data bits as either a high or lowresistance state. One such memory, magnetic random access memory (MRAM),features non-volatility, fast writing/reading speed, almost unlimitedprogramming endurance and zero standby power. The basic component ofMRAM is a magnetic tunneling junction (MTJ). MRAM switches the MTJresistance by using a current induced magnetic field to switch themagnetization of MTJ. Current induced spin-torque may alternately beused to switch the magnetization of an MTJ in STRAM memories. As the MTJsize shrinks, the switching magnetic field amplitude increases and theswitching variation becomes more severe.

However, many yield-limiting factors must be overcome before suchmagnetic stacks can reliable be used as memory devices or field sensors.Therefore, magnetic stacks with increased layer uniformity are desired.One concern in traditional STRAM design is the thickness tradeoff of thefree layer of the STRAM cell. A thicker free layer improves the thermalstability and data retention but also increases the switching currentrequirement since it is proportional to the thickness of the free layer.Thus, the amount of current required to switch the STRAM cell betweenresistance data states is large.

BRIEF SUMMARY

The present disclosure relates to a magnetic stack, such as a spintorque memory cell, or magnetic tunnel junction cell, that has amultilayer laminated free layer.

One particular embodiment of this disclosure is a magnetic stackcomprising a multilayer free layer having a switchable magnetizationorientation, the free layer comprising a first ferromagnetic portion anda second ferromagnetic portion, with an electrically conductingnon-magnetic intermediate layer between the first portion and the secondportion. The magnetic stack also includes a first ferromagneticreference layer having a pinned magnetization orientation, a firstnon-magnetic spacer layer between the free layer and the first referencelayer, a second ferromagnetic reference layer having a pinnedmagnetization orientation, and a second non-magnetic spacer layerbetween the free layer and the second reference layer.

These and various other features and advantages will be apparent from areading of the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1A is a side view diagram of an illustrative magnetic stack, inparticular, a magnetic memory cell with in-plane magnetizationorientation in a low resistance state; FIG. 1B is schematic side viewdiagram of the illustrative magnetic stack in a high resistance state;

FIG. 2 is a schematic diagram of an illustrative memory unit including amemory cell and a semiconductor transistor;

FIG. 3 is a schematic diagram of an illustrative memory array;

FIG. 4 is a side view diagram of an illustrative magnetic stack havingdual reference layers;

FIG. 5 is a graphical representation of an M-H curve for the free layerof the magnetic stack of FIG. 4;

FIG. 6 is a side view diagram of a magnetic stack having dual referencelayers and a laminated free layer;

FIG. 7 is a graphical representation of an M-H curve for the free layerof the magnetic stack of FIG. 6; and

FIG. 8 is a side view diagram of another magnetic stack having dualreference layers and a laminated free layer.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the sameor similar number.

DETAILED DESCRIPTION

This disclosure is directed to magnetic stacks (e.g., spin torque memory(STRAM) cells and read sensors) that include an electrically conductiveintermediate material within the ferromagnetic free layer. By includingsuch an intermediate layer within the free layer in a magnetic stackhaving dual reference layers, the consistency and smoothness of variouslayers of the stack are improved, reducing interlayer coupling.

In the following description, reference is made to the accompanying setof drawings that form a part hereof and in which are shown by way ofillustration several specific embodiments. It is to be understood thatother embodiments are contemplated and may be made without departingfrom the scope or spirit of the present disclosure. The followingdetailed description, therefore, is not to be taken in a limiting sense.Any definitions provided herein are to facilitate understanding ofcertain terms used frequently herein and are not meant to limit thescope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

It is noted that terms such as “top”, “bottom”, “above, “below”, etc.may be used in this disclosure. These terms should not be construed aslimiting the position or orientation of a structure, but should be usedas providing spatial relationship between the structures.

FIGS. 1A and 1B are cross-sectional schematic diagrams of anillustrative magnetic stack 10. In some embodiments, magnetic stack 10is a magnetic read sensor such as a magnetic read sensor used in arotating magnetic storage device. In other embodiments, magnetic stack10 is a magnetic memory cell and may be referred to as a magnetic tunneljunction cell (MTJ), variable resistive memory cell or variableresistance memory cell or the like.

Magnetic stack 10 includes a relatively soft ferromagnetic free layer 12and a ferromagnetic reference (i.e., fixed or pinned) layer 14.Ferromagnetic free layer 12 and ferromagnetic reference layer 14 areseparated by an electrically insulating and non-magnetic barrier layer,such as an oxide barrier layer 13. Other layers, such as seed or cappinglayers, are not depicted for clarity. Any or all of layers 12, 13, 14may be made by thin film techniques such as chemical vapor deposition(CVD), physical vapor deposition (PVD), and atomic layer deposition(ALD).

Free layer 12 and reference layer 14 each have an associatedmagnetization orientation; the magnetization orientation of free layer12 being more readily switchable than the magnetization orientation ofreference layer 14. In some embodiments, proximate ferromagneticreference layer 14 is an antiferromagnetic (AFM) pinning layer that pinsthe magnetization orientation of reference layer 14 by exchange biaswith the antiferromagnetically ordered material of the pinning layer.Examples of suitable pinning materials include PtMn, IrMn, and others.In alternate embodiments, other mechanisms or elements may be used topin the magnetization orientation of reference layer 14. In theillustrated embodiment, free layer 12 is above reference layer 14; inother embodiments, reference layer 14 may be above free layer 12.

Ferromagnetic layers 12, 14 may be made of any useful ferromagnetic (FM)material such as, for example, Fe, Co or Ni and alloys thereof, such asNiFe and CoFe. Ternary alloys, such as CoFeB, may be particularly usefulbecause of their lower moment and high polarization ratio. Either orboth of free layer 12 and reference layer 14 may be either a singlelayer or an unbalanced synthetic antiferromagnetic (SAF) coupledstructure, i.e., two ferromagnetic sublayers separated by a metallicspacer, such as Ru or Cr, with the magnetization orientations of thesublayers in opposite directions to provide a net magnetization. Barrierlayer 13 is made of an electrically insulating material such as, forexample an oxide material (e.g., Al₂O₃, TiO, or MgO). Barrier layer 13could optionally be patterned with free layer 12 or with reference layer14, depending on process feasibility and device reliability.

A first electrode 18 is in electrical contact with ferromagnetic freelayer 12 and a second electrode 19 is in electrical contact withferromagnetic reference layer 14. Electrodes 18, 19 electrically connectferromagnetic layers 12, 14 to a control circuit providing read and/orwrite currents through layers 12, 14. The resistance across magneticstack 10 is determined by the relative orientation of the magnetizationvectors or magnetization orientations of ferromagnetic layers 12, 14.The magnetization direction of reference layer 14 is pinned in apredetermined direction while the magnetization direction offerromagnetic free layer 12 is free to rotate, for example, under theinfluence of a magnetic field or under the influence of spin torque.

In FIG. 1A, magnetic stack 10 is in the low resistance state where themagnetization orientation of free layer 12 is parallel and in the samedirection as the magnetization orientation of reference layer 14. Thisis termed the low resistance state. In FIG. 1B, magnetic stack 10 is inthe high resistance state where the magnetization orientation of freelayer 12 is anti-parallel and in the opposite direction of themagnetization orientation of reference layer 14. This is termed the highresistance state. In some embodiments, the low resistance staterepresents data state “0” and the high resistance state represents datastate “1”, whereas in other embodiments, the low resistance state is “1”and the high resistance state is “0”.

Switching the resistance state and hence the data state of magneticstack cell 10 (e.g., when magnetic stack 10 is a magnetic memory cell,such as a magnetic tunnel junction cell) may be done via spin-transferwhen a current, passing through a magnetic layer of magnetic stack 10,becomes spin polarized and imparts a spin torque on free layer 12. Whena sufficient spin torque is applied to free layer 12, the magnetizationorientation of free layer 12 can be switched between two oppositedirections and accordingly, magnetic stack 10 (e.g., magnetic tunneljunction memory cell) can be switched between the parallel state (i.e.,low resistance state) and anti-parallel state (i.e., high resistancestate).

In other embodiments, such as when stack 10 is a magnetic reader head,the magnetization orientation of free layer 12 is influenced by amagnetic field located on a magnetic recording medium proximate thereader head. When a sufficient magnetic field is applied to free layer12, the magnetization orientation of free layer 12 can be changed amongdifferent directions, between the parallel state, the anti-parallelstate, and other states.

FIG. 2 is a schematic diagram of an illustrative memory unit 20including a memory element 21 electrically coupled to a semiconductortransistor 22 via an electrically conducting element. Memory element 21may be a memory cells described herein, or may be any other magneticmemory cell. Transistor 22 includes a semiconductor substrate 25 havingdoped regions (e.g., illustrated as n-doped regions) and a channelregion (e.g., illustrated as a p-doped channel region) between the dopedregions. Transistor 22 includes a gate 26 that is electrically coupledto a word line WL to allow selection and current to flow from a bit lineBL to memory element 21. An array of programmable metallization memoryunits 20 can be formed on a semiconductor substrate utilizingsemiconductor fabrication techniques.

FIG. 3 is a schematic diagram of an illustrative memory array 30. Memoryarray 30 includes a plurality of word lines WL and a plurality of bitlines BL forming a cross-point array. At each cross-point a memoryelement 31 is electrically coupled to word line WL and bit line BL.Memory element 31 may be any of the memory cells described herein, ormay be any other magnetic memory cell.

Magnetic memory cells (such as those of FIGS. 1A and 1B) having a datastate switchable by spin torque, generally have an in-plane anisotropyof 2πMs. For a free layer 12 composed of NiFe, the in-plane anisotropicfield is around 5000 Oe. However, the uni-axial anisotropic field, whichstabilizes the cell against thermal excitations and provides the longterm data retention, is only around 500 Oe. If the in-plane anisotropycan be reduced while increasing the uni-axial anisotropy field, one canobtain ST RAM cells that switch easier (i.e., with less switchingcurrent) yet have higher thermal stability and better retention.Magnetic stacks having dual reference layers with a free layer having alow saturated magnetic moment (Ms) are one means to reduce the switchingcurrent.

FIG. 4 is an illustrative magnetic stack 40 having dual or twoferromagnetic reference layers having a pinned magnetization orientationwith a ferromagnetic free layer therebetween. In general, the variouselements, features and materials of magnetic stack 40 are the same as orsimilar to the various elements, features and materials of magneticstack 10 of FIGS. 1A and 1B, unless indicated otherwise.

Magnetic stack 40 has a relatively soft ferromagnetic free layer 42, afirst ferromagnetic reference (i.e., fixed or pinned) layer 44 and asecond ferromagnetic reference (i.e., fixed or pinned) layer 46. Secondreference layer 46 may be the same as or different than first referencelayer 44, for example, in material and/or thickness. Free layer 42 andfirst reference layer 44 are separated by an electrically insulating andnon-magnetic barrier layer 43, and free layer 42 and second referencelayer 46 are separated by a second electrically insulating andnon-magnetic barrier layer 45. Second barrier layer 45 may be the sameas or different than first barrier layer 43, for example, in materialand/or thickness. Other layers, such as seed or capping layers, orpinning layers, are not depicted for clarity. Also not illustrated arethe electrodes electrically connected to layers 42, 44, 46.

Ferromagnetic layers 42, 44, 46 may be made of any useful ferromagnetic(FM) material such as, for example, Fe, Co or Ni and alloys thereof,such as NiFe, CoFe, and CoFeB. Any or all of free layer 42 and referencelayers 44, 46 may be either a single layer or an unbalanced syntheticantiferromagnetic (SAF) coupled structure. In some embodiments,ferromagnetic layers 42, 44,46, particularly free layer 42, is formed ofa ferromagnetic material with acceptable anisotropy and a saturationmoment (Ms) that is at least 1000 emu/cc, often at least 1100 emu/cc,and in some embodiments at least 1500 emu/cc, where emu refers toelectromagnetic unit of magnetic dipole moment and cc refers to cubiccentimeter. In many embodiments, free layer 42 isCo_(100-X-Y)Fe_(X)B_(Y), wherein X is greater than 30 and Y is greaterthan 15. Barrier layers 43, 45 are made of electrically insulatingmaterials such as, for example an oxide material (e.g., Al₂O₃, TiO, orMgO).

Free layer 42 and reference layers 44, 46 each have an associatedmagnetization orientation; the magnetization orientation of free layer42 being more readily switchable than the magnetization orientation ofreference layers 44, 46. The resistance across magnetic stack 40, andthus data state, is determined by the net relative orientation of themagnetization vectors or magnetization orientations of ferromagneticlayers 42, 44, 46. In FIG. 4, the magnetization orientations ofreference layers 44, 46 are opposite to one another. Interlayer couplingon free layer 42 from reference layer 44 is compensated by theinterlayer coupling on free layer 42 from reference layer 46. In FIG. 4,the magnetization orientation of free layer 42 is shown as undefined.For ST RAM memory cells, a switching current is passed through cell 40to switch the magnetization orientation of free layer 42 from onedirection to the other.

Magnetic stacks having dual reference layers, such as magnetic stack 40,with a free layer having a low saturated magnetic moment (Ms) are onemeans to reduce the needed switching current. As the magnetic momentdecreases, so does the thermal barrier energy. To implement the reducedswitching current, low area resistance (RA) of free layer 42 is desired,usually less than about 100 Ohm/μm²; low RA, however, needs a very thinbarrier layer 43, 45 (e.g., no more than about 2 nm, e.g., 0.5 to 1.5nm). The thin barrier layer 43, 45 results in large interlayer couplingbetween reference layer 44 and free layer 42 and reference layer 46 andfree layer 42, respectively, which is undesired. In order to reduce theoffset field from the larger interlayer coupling, a static field fromreference layer 46 is required. However, the static field is dependenton the size of cell 40, and any size variation can cause undesiredvariation in the offset field.

Magnetic stacks having dual reference layers, such as magnetic stack 40,with a free layer having a high saturated magnetic moment (Ms) areanother means to reduce the needed switching current while maintaininghigh thermal stability. In order to achieve high magnetic resistance,crystalline materials (e.g., crystalline MgO) are preferred materialsfor barrier layer 43 and/or barrier layer 45.

Magnetic stack 40 is manufactured in a bottom to top manner, with thebottom most layer (i.e., first reference layer 44) being formed beforeany upper layer (i.e., barrier layer 43, free layer 42, etc.). It is notuncommon that the application (e.g., deposition) of crystalline materialfor first barrier layer 43 results in barrier layer 43 having anon-uniform or rough surface, based on the various factors of barrierlayer 43, such as its material, process of forming layer 43, andthickness of layer 43. In most embodiments, this roughness is on anatomic or molecular scale. Over barrier layer 43 is applied (e.g.,deposited) free layer 42. The rough surface of layer 43 results in aninterface 47 between barrier layer 43 and free layer 42 that is notsmooth, but has a roughness associated therewith. This roughness iscarried through free layer 42. When second barrier layer 45 and secondreference layer 46 are subsequently deposited over free layer 42, therough interface 48 between free layer 42 and second barrier layer 45will cause large interlayer coupling between second reference layer 46and free layer 42.

In addition to the undesired large interlayer coupling, the roughsurface of first barrier layer 43 can result in non-uniform thicknessesof any or all of first barrier layer 43, free layer 42, second barrierlayer 45 and even second reference layer 46. This is particularly anissue if barrier layer 43 is thin (e.g., less than about 1 nm), asneeded for low area resistance requirement (e.g., less than about 50Ohms/μm²), as pin holes in layer 43 may occur.

FIG. 5 illustrates a graphical representation of the magnetization(M)-magnetic field (H) curve of free layer 42 of dual structure magneticstack 40, when first barrier layer 43 is crystalline MgO at a thicknessof about 10 Angstroms and second barrier layer 45 is crystalline MgO ata thickness of about 12 Angstroms. The two curves representing theforward and backward switching of the free layer magnetization. Ingeneral, the interlayer coupling decreases as the thickness of either orboth barrier layers 43, 45 increases. Additionally, as the thickness offree layer 42 increases, the interlayer coupling decreases.

FIG. 6 illustrates a dual reference layer magnetic stack having amultilayer laminated free layer, which addresses the issues describedabove. In general, the various elements, features and materials ofmagnetic stack 60 of FIG. 6 are the same as or similar to the variouselements, features and materials of magnetic stack 40 of FIG. 4, unlessindicated otherwise.

Magnetic stack 60 has a relatively soft ferromagnetic free layer 62, afirst ferromagnetic reference (i.e., fixed or pinned) layer 64 and asecond ferromagnetic reference (i.e., fixed or pinned) layer 66, whichmay be the same as or different than first reference layer 64. Freelayer 62 and first reference layer 64 are separated by a firstelectrically insulating and non-magnetic barrier layer 63, and freelayer 62 and second reference layer 66 are separated by a secondelectrically insulating and non-magnetic barrier layer 65, which may bethe same or different than first barrier layer 63.

Ferromagnetic free layer 62 is a multilayer layer, composed of at leasttwo different materials present as discrete layers. Free layer 62includes an electrically conducting, non-magnetic intermediate layer 67,which divides and separates free layer 62 into a first portion 62A and asecond portion 62B. First portion 62A and second portion 62B remainstrongly ferromagnetically coupled. Together, intermediate layer 67,first portion 62A and second portion 62B are referred to as a multilayerfree layer, a laminated free layer, a laminated multilayer, andvariations thereof. In some embodiments, free layer 62 may be referredto as a sandwich structure.

The presence of intermediate layer 67 does not modify the totalthickness of ferromagnetic material (i.e., first portion 62A and secondportion 62B) by more than about 5 Angstroms, thus, allowing the same orsimilar magnetic resistance has if no intermediate layer 67 werepresent. Free layer portions 62A and 62B may have the same or differentthicknesses. In most embodiments, intermediate layer 67 is at or closeto the center of free layer 62, so that first portion 62A and secondportion 62B differ in thickness by no more than about 25%, often no morethan about 10%. In some embodiments, portion 62A and 62B may be the sameferromagnetic material whereas in other embodiments, free layer portion62A and 62B are formed of different ferromagnetic materials.

Intermediate layer 67 can be any useful electrically conducting andnon-ferromagnetic material such as, for example, Ru, Ta, Pd, Cr, RuO orPt. Intermediate layer 67 has an area resistance less than about 100Ohms/μm². The thickness of intermediate layer 67 is usually about 2 to 5Angstroms.

Intermediate layer 67 has at least two desired functions. The first isto provide a physical break within free layer 62, forming first portion62A and second portion 62B. By having the electrically conducting,non-magnetic intermediate layer 67 within free layer 62, the upper,second portion 62B does not follow the crystalline structure of firstbarrier layer 63 nor the structure of first portion 62A. Because ofthis, second portion 62B can be a ferromagnetic material different thanthat of first portion 62A, selected to, for example, to modify the othermagnetic properties, such as magneto-striction, or coercivity withoutsacrificing the magneto-resistance. As an example, ferromagnetic firstportion 62A may have a high saturation magnetization, such as 1100emu/cc, while ferromagnetic second portion 62B has a low saturationmagnetization, such as 500 emu/cc.

A second effect of intermediate layer 67 is to inhibit the rough surfaceof barrier layer 63 from being continued through free layer 62, as seenin FIG. 6. First barrier layer 63 has a rough upper surface, which istranslated to the upper surface of free layer first portion 62A. Due to,at least, the surface energy and molecular structure of intermediatelayer 67, intermediate layer 67 evens out the rough surface, providing agenerally smooth surface for free layer second portion 62B. Materialfrom intermediate layer 67 has a desire to settle in crevices and otherlow regions of any rough surface, thus filling and leveling the roughsurface; in some embodiments, this may be referred to as “dusting”.

Second barrier layer 65 may be amorphous or crystalline.

FIG. 7 illustrates a graphical representation of the magnetization(M)-magnetic field (H) curve of multilayer free layer 62 of dualstructure magnetic stack 60, the two curves representing the forward andbackward switching of the free layer magnetization. For this embodiment,first barrier layer 63 is crystalline MgO at a thickness of about 10Angstroms and second barrier layer 65 is crystalline MgO at a thicknessof about 9.5 Angstroms. Because of the smooth interface between secondportion 62B and second barrier layer 65, a thinner barrier layer 65 canbe used. A thinner barrier can also reduce the area resistance (RA). Bycomparing FIG. 7 with FIG. 5, it is seen that by having a multilayerfree layer (e.g., free layer 62) the smoothness of the magnetization isincreased with laminated free layer 62.

FIG. 8 illustrates an alternate embodiment of a dual reference layermagnetic stack 80 having a multilayer laminated free layer. In thisembodiment, the reference layer has two or more pinned ferromagneticlayers, which are strongly coupled antiferromagnetically. This referencemultilayer is further fixed by an antiferromagnetic (AFM) layer. Ingeneral, the various elements, features and materials of magnetic stack80 of FIG. 8 are the same as or similar to the various elements,features and materials of magnetic stack 40 of FIG. 4 and magnetic stack60 of FIG. 6, unless indicated otherwise.

Magnetic stack 80 has a relatively soft ferromagnetic multilayer freelayer 82, a first ferromagnetic reference (i.e., fixed or pinned) layer84 and a second ferromagnetic reference (i.e., fixed or pinned) layer86, which may be the same as or different than first reference layer 84.Free layer 82 and first reference layer 84 are separated by a firstelectrically insulating and non-magnetic barrier layer 83, and freelayer 82 and second reference layer 86 are separated by a secondelectrically insulating and non-magnetic barrier layer 85, which may bethe same or different than first barrier layer 83.

Ferromagnetic free layer 82 is a multilayer layer, composed of anelectronically conducting, non-magnetic intermediate layer 87 thatdivides and separates free layer 82 into a first portion 82A and asecond portion 82B. Together, intermediate layer 87, first portion 82Aand second portion 82B are referred to as multilayer free layer 82,laminated free layer 82, laminated multilayer 82, and variationsthereof. In some embodiments, free layer 82 may be referred to as asandwich structure.

In this embodiment, first reference layer 84 is a multilayer unbalancedsynthetic antiferromagnetic (SAF) coupled structure, i.e., twoferromagnetic sublayers separated by a metallic spacer, such as Ru, Pdor Cr, with the magnetization orientations of the sublayers in oppositedirections to provide a net magnetization. A multilayer SAF has morethan one coupled structure. In FIG. 8, reference layer 84 has a firstferromagnetic sublayer 842 separated from a second ferromagneticsublayer 844 by a first metallic spacer 843, and also has a thirdferromagnetic sublayer 846 separated from second ferromagnetic sublayer844 by a second metallic spacer 845. Included in reference layer 84 isan antiferromagnetic (AFM) pinning layer 848, which pins themagnetization orientation of ferromagnetic sublayer 842 by exchange biaswith the antiferromagnetically ordered material of pinning layer 848.Examples of suitable pinning materials include PtMn, IrMn, and others.In alternate embodiments, other mechanisms or elements may be used topin the magnetization orientation of sublayer 842 or of reference layer84.

Second reference layer 86 is a single, unbalanced syntheticantiferromagnetic (SAF) coupled structure, i.e., two ferromagneticsublayers separated by a metallic spacer, such as Ru, Pd or Cr, with themagnetization orientations of the sublayers in opposite directions toprovide a net magnetization. Reference layer 86 has a firstferromagnetic sublayer 862 separated from a second ferromagneticsublayer 864 by a metallic spacer 863. Included in reference layer 86 isan antiferromagnetic (AFM) pinning layer 868, which pins themagnetization orientation of ferromagnetic sublayer 864 by exchange biaswith the antiferromagnetically ordered material of pinning layer 868.Other mechanisms or elements may be used to pin the magnetizationorientation of sublayer 864 or of reference layer 86.

In one particular embodiment, magnetic stack 80 includes ferromagneticfree layer portions 82A, 82B both formed from CoFeB having a saturatedmagnetic moment (Ms) of about 1100 emu/cc. Intermediate layer 87 betweenCoFeB portions 82A, 82B is Ta, Ru or Cr. Metallic spacers 843, 845, 863of the SAF structures may be any or all of Ru, Pd, and Cr. Barrierlayers 83, 85 are MgO.

In another particular embodiment, magnetic stack 80 includesferromagnetic free layer portions 82A, 82B, one of which is formed froma ferromagnetic material having a low saturated magnetic moment (Ms) ofabout 500 emu/cc; examples of such materials include NiFe,CO_(100-X-Y)Fe_(X)B_(Y), where X is about 10 and Y is about 20.Intermediate layer 87 between portions 82A, 82B is Ta, Ru or Cr.Metallic spacers 843, 845, 863 of the SAF structures may be any or allof Ru, Pd, and Cr. Barrier layers 83, 85 are MgO.

The magnetic stacks of this disclosure, including any or all of thelayers, may be made by thin film techniques such as chemical vapordeposition (CVD), physical vapor deposition (PVD), and atomic layerdeposition (ALD).

Various other embodiments of a multilayer laminated free layer inmagnetic stacks with dual reference layers are within the scope of thisdisclosure. An electrically conducting, non-magnetic intermediate layerwithin the free layer provides a smooth surface and broken structurebetween two free layer portions. The multilayer provides low arearesistance, improves the uniformity of the second barrier layer, andprovides small interlayer coupling field for the top barrier layer.

Thus, embodiments of the MAGNETIC STACK WITH LAMINATED LAYER aredisclosed. The implementations described above and other implementationsare within the scope of the following claims. One skilled in the artwill appreciate that the present disclosure can be practiced withembodiments other than those disclosed. The disclosed embodiments arepresented for purposes of illustration and not limitation, and thepresent invention is limited only by the claims that follow.

1. A magnetic stack comprising: a first ferromagnetic reference layerhaving a pinned magnetization orientation; a free layer having aswitchable magnetization orientation; a first non-magnetic, electricallyinsulating barrier layer; a second non-magnetic, electrically insulatingbarrier layer; and a second ferromagnetic reference layer having apinned magnetization orientation, wherein the first non-magnetic spacerlayer is positioned between the first ferromagnetic reference layer andthe free layer, the free layer is positioned between the firstnon-magnetic spacer layer and the second non-magnetic spacer layer, andthe second non-magnetic spacer layer is positioned between the freelayer and the second ferromagnetic reference layer.
 2. The magneticstack of claim 1, wherein the first and second barrier layersindependently comprise a crystalline material.
 3. The magnetic stack ofclaim 2, wherein both the first barrier layer and the second barrierlayer comprise crystalline MgO.
 4. The magnetic stack of claim 1,wherein the first and second barrier layers have a thickness of fromabout 0.5 nm to about 1.5 nm.
 5. The magnetic stack of claim 1, whereinthe material of the free layer has a saturation moment (Ms) that is atleast 1000 emu/cc.
 6. The magnetic stack of claim 1, wherein thematerial of the free layer has a saturation moment (Ms) that is at least1500 emu/cc.
 7. The magnetic stack of claim 1, wherein the free layercomprises Co_(100-x-y)Fe_(x)B_(y), wherein x is greater than 30 and y isgreater than
 15. 8. The magnetic stack of claim 1, wherein themagnetization orientations of the first ferromagnetic reference layerand the second ferromagnetic reference layer are opposite to oneanother.
 9. The magnetic stack of claim 1, wherein the first referencelayer comprises an unbalanced synthetic antiferromagnetic coupledstructure.
 10. The magnetic stack of claim 1, wherein the secondreference layer comprises an unbalanced synthetic antiferromagneticcoupled structure.
 11. The magnetic stack of claim 1, wherein themagnetic stack is a magnetic tunnel junction memory cell.
 12. Themagnetic stack of claim 1, wherein the magnetic stack is a magnetic readsensor in a recording head.
 13. A magnetic memory device comprising: asubstrate having a source region and a drain region with a channelregion therebetween; a gate electrically between the channel region anda word line; a magnetic memory cell electrically connected to one of thesource region and the drain region, the magnetic cell comprising: afirst ferromagnetic reference layer having a pinned magnetizationorientation; a free layer having a switchable magnetization orientation;a first non-magnetic, electrically insulating barrier layer; a secondnon-magnetic, electrically insulating barrier layer; and a secondferromagnetic reference layer having a pinned magnetization orientation,wherein the first non-magnetic spacer layer is positioned between thefirst ferromagnetic reference layer and the free layer, the free layeris positioned between the first non-magnetic spacer layer and the secondnon-magnetic spacer layer, and the second non-magnetic spacer layer ispositioned between the free layer and the second ferromagnetic referencelayer; a first line electrically connected to the magnetic memory cell;and a second line electrically connected to the other of the sourceregion and the drain region.
 14. The magnetic stack of claim 13, whereinthe first and second barrier layers independently comprise a crystallinematerial.
 15. The magnetic stack of claim 13, wherein both the firstbarrier layer and the second barrier layer comprise crystalline MgO. 16.The magnetic stack of claim 13, wherein the first and second barrierlayers have a thickness of from about 0.5 nm to about 1.5 nm.
 17. Themagnetic stack of claim 13, wherein the material of the free layer has asaturation moment (Ms) that is at least 1500 emu/cc.
 18. The magneticstack of claim 13, wherein the free layer comprisesCO_(100-x-y)Fe_(x)B_(y), wherein x is greater than 30 and y is greaterthan
 15. 19. The magnetic stack of claim 1, wherein the magnetizationorientations of the first ferromagnetic reference layer and the secondferromagnetic reference layer are opposite to one another.
 20. Aspin-torque magnetic memory device comprising: a substrate having asource region and a drain region with a channel region therebetween; agate electrically between the channel region and a word line; a magneticmemory cell electrically connected to one of the source region and thedrain region, the magnetic cell comprising: a first ferromagneticreference layer having a pinned magnetization orientation; a free layerhaving a switchable magnetization orientation; a first non-magnetic,electrically insulating barrier layer; a second non-magnetic,electrically insulating barrier layer; and a second ferromagneticreference layer having a pinned magnetization orientation, wherein thefirst non-magnetic spacer layer is positioned between the firstferromagnetic reference layer and the free layer, the free layer ispositioned between the first non-magnetic spacer layer and the secondnon-magnetic spacer layer, and the second non-magnetic spacer layer ispositioned between the free layer and the second ferromagnetic referencelayer, wherein the magnetic memory cell has a resistance state, whichcan be switched via spin-transfer by passing a current through themagnetic memory cell; a first line electrically connected to themagnetic memory cell; and a second line electrically connected to theother of the source region and the drain region.